1. Field of the Invention
This invention relates to a vehicle meter self-diagnosis apparatus for diagnosing a condition such as a broken line or a short circuit of vehicle electric analog meters each using a cross coil movement and a method of starting a self-diagnosis mode of the self-diagnosis apparatus.
2. Description of the Related Art
If a meter seems to fail, a self-diagnosis apparatus is used to carry out a diagnosis for determining a failure place (the meter or a sensor) at a dealer or a service garage.
An apparatus shown in FIG. 11 is known as such a conventional vehicle meter self-diagnosis apparatus, for example, as disclosed in Japanese Utility Model Laid-Open No. Sho 62-195776. FIG. 11 is a circuit diagram to show a conventional vehicle meter self-diagnosis apparatus. FIG. 12 is a block diagram of a conventional self-diagnosis start control circuit. FIG. 13 is a block diagram of a conventional odo/trip signal processing circuit.
In FIG. 11, numeral 100 is an incorporated pseudo signal generation circuit, numeral 101 is a speed signal, numerals 102 and 104 are input circuits, numeral 103 is an engine rotation signal, numeral 105 is a fuel remaining amount signal, numeral 106 is a water temperature signal, numeral 107 is an A/D (analog-digital) converter, numeral 108 is a CPU (central processing unit) for performing signal processing, operations, etc., numeral 109 is an LCD (liquid crystal display) for producing odd/trip display, and numeral 110 is a driver for driving the LCD 109.
Numeral 111 is a speed meter made up of components such as a cross coil movement having a pair of coils placed so as to cross each other at an angle of 90 degrees and a moving magnet for indication placed rotatably under a magnetic field produced by the coils, numeral 112 is a driver for driving the speed meter 111, numeral 113 is a tachometer, numeral 114 is a driver for driving the tachometer 113, numeral 115 is a fuel gauge, numeral 116 is a driver for driving the fuel gauge 115, numeral 117 is a water temperature gauge, and numeral 118 is a driver for driving the water temperature gauge 117.
Numeral 120 is a driver control circuit for controlling the drivers 112, 114, 116, and 118 and numeral 122 is a ROM (read-only memory) of a nonvolatile memory into which indication adjustment information such as pointer swing angles of the speed meter 111, the tachometer 113, the fuel gauge 115, and the water temperature gauge 117 are written. Numeral 132 is an odd/trip meter reset switch.
In FIG. 12, numeral 140 is a self-diagnosis start control circuit being provided in the CPU 108 for the odo/trip LCD 109, the speed meter 111, the tachometer 113, the fuel gauge 115, and the water temperature gauge 117.
The self-diagnosis start control circuit 140 comprises a power supply sequence connected to a battery 150 via a power supply circuit 152, an odd/trip signal processing circuit 142 for performing predetermined signal processing to produce odd/trip display on the LCD 109, and an LCD driver interface 143 of an interface to the driver 110. Numeral 154 is an ignition switch.
As shown in FIG. 13, the odd/trip signal processing circuit 142 comprises a sensing section 142a for sensing that the ignition switch 154 is on or off and a data output section 142b for outputting segment data to the LCD driver interface 143 in response to output of the sensing section 142a. The output of the sensing section 142a is connected to the pseudo signal generation circuit 100.
Next, the operation will be discussed.
FIG. 14 is a flowchart to show the operation of the conventional vehicle meter self-diagnosis apparatus. While the reset switch 132 is turned on with the battery 150 on, the ignition switch 154 is turned on at step ST1. Then, the sensing section 142a senses that the ignition switch 154 is turned on, and control goes to step ST2.
If the reset switch 132 is not turned on and the ignition switch 154 is not turned on either, the LCD 109 does not go on. If the reset switch 132 is not turned on and the ignition switch 154 is turned on, the vehicles enter the normal operation mode.
At step ST2, the data output section 142b outputs predetermined segment data to the LCD driver interface 143 and the LCD driver interface 143 and the driver 110 check the LCD 109 for segments.
In the cross coil movement, the pseudo signal generation circuit 100 is also started by the operation and shifts to the self-diagnosis mode and the speed meter 111 the tachometer 113, the fuel gauge 115, and the water temperature gauge 117 are operated in response to indication adjustment information such as swing angles and sweep time preset as pseudo signals in the pseudo signal generation circuit 100. whether or not a failure occurs is determined according to the operation information.
An apparatus shown in FIG. 15 is known as another conventional vehicle meter self-diagnosis apparatus. In the figure, numeral 160 is a pseudo signal generator connected from the outside. Other components and the operation are similar to those in the conventional example described above and will not be discussed again.
Since the conventional vehicle meter self-diagnosis apparatus is thus configured, the input circuits 102 and 104, the A/D converter 107, the CPU 108, and the like with a large number of circuit elements and a high failure probability must be used to start the self-diagnosis mode. If the circuit itself fails, which of the circuit or the cross coil movement fails cannot be determined and the reliability of the self diagnosis is degraded.
Since the self-diagnosis mode is started only by turning on both the reset switch 132 and the ignition switch 154 at the same time, there is a possibility that general users will starts the self-diagnosis mode by mistake. Once the self-diagnosis mode is started by mistake, the meters are determined to fail.
Further, to use the pseudo signal generator 160 to carry out a self-diagnosis, the vehicle meters must be removed to input predetermined signals; it is difficult to carry out an easy and prompt diagnosis.